This invention relates to a solid-state image pickup device for use in picking up image and, more particularly, to a solid-state image pickup device comprising power feeding wires, which serve as light-shield films, for supplying clock pulses to charge transfer electrodes provided along columns of photoelectric converting sections.
In comparison with image pickup tubes generally used in prior art, solid-state image pickup devices are superior in small-sized, lightweight, high durability, low power consumption, low afterimage, low burning, and so on. As a result, the solid-state image pickup devices already surpass the image pickup tubes in a camera field for public use where movie cameras have small image size. Furthermore, the solid-state image pickup devices replace in a camera field for business use where cameras have relatively large image size.
Solid-state image pickup devices for a high-definition television (HDTV) are typical of the solid-state image pickup devices having the relatively large image size, for example, solid-state image pickup devices having an optical size of one inch or two-thirds inches. In such solid-state image pickup devices, driving pulses are generally supplied to transfer electrodes of polysilicon in both sides of an image region. The transfer electrodes of polysilicon are commonly disposed in all of one horizontal line. In the solid-state image pickup devices of such a driving pulse supplying method, the transfer electrodes of polysilicon have relatively high resistance and relatively high capacitance. As a result, such solid-state image pickup devices are disadvantageous in that pulse amplitude of the driving pulses remarkably decreases in a central portion of the image region and the amount of maximum transferring charges decreases especially when a transfer speed is fast.
In order to overcome the above-mentioned disadvantage, proposal has been made by Toshihida Nobusada et al in a paper submitted to "1989 IEEE International Solid-State Circuits Conference" as Paper No. WPM 8.1, pages 88-89, Feb. 15, 1989 under the title of "Frame Interline Transfer CCD Sensor for HDTV Camera."
The solid-state image pickup device of an interline transfer type generally comprises photoelectric converting sections for converting incident light into signal charges, vertical charge transfer sections for reading the signal charges out of the photoelectric converting sections as read charges to transfer the read charges along a vertical direction as vertical transferred charges, a horizontal charge transfer section for receiving the vertical transferred charges from the vertical charge transfer sections horizontal line by horizontal line as received charges to transfer along a horizontal direction as horizontal transferred charges, and an output circuit section for converting the horizontal transferred charges into a voltage signal. Those components are isolated from one another by element isolation sections.
In a conventional solid-state pickup device disclosed by Nobusada et al, a p-type well layer is formed in an n-type semiconductor substrate. The p-type well layer has a surface area in which the photoelectric converting sections, charge transfer regions of the vertical transfer sections, and element isolation sections are formed. Each of the photoelectric converting sections consists of an n-type semiconductor region and a p.sup.+ -type semiconductor region. Each of the charge transfer regions consists of an n-type semiconductor region. The element isolation sections comprises p.sup.+ -type semiconductor regions. On those regions through an insulation film, a plurality of transfer electrodes of the vertical charge transfer sections and a plurality of power feeding wires are formed. The transfer electrodes are made of polycrystalline silicon and are classified into first and second vertical charge transfer electrodes. The power feeding wires are classified into first through fourth metal wires. The power feeding wires supply clock pulses to the transfer electrodes and serve as light-shield films. The first through the fourth metal wires are formed by a single layer.
The first through the fourth metal wires are formed every four vertical charge transfer sections and are connected to the transfer electrodes through contact holes. The first and the second vertical charge transfer electrodes are adjacent to picture elements in one horizontal line in common and connected to the power feeding wires every four picture elements along a horizontal direction.
The conventional solid-state image pickup device is driven by applying the clock pulses of first through fourth clock pulse signals to the first through the fourth metal wires, respectively. The vertical charge transfer electrodes are supplied with reading pulses having high voltage through the second and the fourth metal wires, whereby reading of the signal charges is carried out from the photoelectric converting sections to the vertical charge transfer sections.
Inasmuch as the first through the fourth metal wires serves as the light-shield films, they extend on the photoelectric converting sections with passing the second vertical charge transfer electrodes. As a result, the reading pulse having the high positive voltage is supplied to the second vertical charge transfer electrodes via the second or the fourth metal wires, the p.sup.+ -type semiconductor regions deplete to form a local potential well, which results in degradation of a readout characteristic of the signal charges.
When the local potential well is minimized by narrowing the amount of overlapping between the second and the fourth metal wires and the photoelectric converting sections, smear characteristic degrades because spurious signal charges flowing the vertical charge transfer sections increase.
Inasmuch as it is necessary for the conventional solid-state image pickup device to connect the first and the second vertical charge transfer electrodes between the adjacent photoelectric converting sections in the vertical direction by first and second connecting electrode lines, respectively, the first and the second connecting electrode lines must be laminated to each other at laminated areas. As a result, large capacitance is formed between the first and the second vertical charge transfer electrodes. In addition, capacitance is formed at the laminated area between the n-type semiconductor substrate and the first charge transfer electrodes. As a result, bluntness of waveform of the clock pulses occurs, which results in degradation of transfer characteristic for the vertical charge transfer sections.